The lower-left quadrant outlines how the sheet metal sheets must be machined or formed to accept the fastener. This is vital for maintaining aerodynamic flushness or joint strength. : Countersunk hole. D : Dimpled hole.
The sheet metal is too thin to countersink, requiring a die to press a dimple into the skin. nas523 rivet code pdf
This quadrant uses a two-letter code to represent the industry specification (like Military Standards (MS) or National Aerospace Standards (NAS) ) and the material alloy. BJ: MS20470AD (Universal head, 2117 aluminum). BB: MS20426AD (100° Countersunk head, 2117 aluminum). 2. Northeast (NE): Diameter & Head Side The lower-left quadrant outlines how the sheet metal